A method of the general class to which the invention relates is disclosed in German Patent Specification No. A-27 52 323. In this method a stream of cooling air is extracted from the cooler and divided into a plurality of branch streams which are introduced at different peripheral points into a kiln exhaust gas duct which forms a material precalcination zone and through which the kiln exhaust gases flow. Corresponding proportions of the material preheated in the precalcination zone are introduced into the branch streams of cooling air immediately before they enter the kiln exhaust gas duct.
The object of this invention is to improve the known method so as to achieve an improvement in the combustion of the fuel and an increase in the rate of combustion.
This object is achieved according to the invention by causing the cooling air streams to be subjected to rotation prior to their introduction to the exhaust gas duct.
The rotation to which the two branch streams of cooling air are subjected before entering the kiln exhaust gas duct results in an intensification of the intermixing of material, fuel, and cooling air in the precalcination zone and thus a marked improvement in the combustion of the fuel and an increase in the rate of combustion.